Chemistry of Life

Chemistry of Life

• Key terms to understand include atom, element, molecule, and compound
• The structure of an atom needs describing
• Recognize elements of the human body from their chemical symbols
• Distinguish between elements and compounds
• Ionic and covalent types of chemical bonding should be compared and contrasted
• Distinguish between organic and inorganic chemical compounds
• Chemical characteristics of water should be discussed
• Need to define acid, a base and the concept of pH
• The structure and function of carbohydrate, lipid, protein, and nucleic acid organic molecules needs discussing

Levels of Chemical Organization

• The body is made of many chemicals
• Chemicals are in the form of molecules
• Molecules are composed of atoms
• Atoms contain subatomic particles including Protons, Neutrons, and Electrons

Components of an Atom

• The nucleus is the central core of the atom
• Energy levels (orbitals) are regions surrounding the atom’s nucleus and contain electrons

Nucleus

• Protons are positively charged particles
• Neutrons are neutral particles in the nucleus
• Atomic number refers to the total number of protons in the nucleus and determines the type of atom
• Atomic mass equals the number of protons + neutrons

Energy Levels (Orbitals)

• Electrons are negatively charged particles
• The level closest to the nucleus contains up to two electrons
• The remaining levels contain up to eight electrons
• Energy increases with distance from the nucleus

Elements, Molecules, and Compounds

• An element is a pure substance made up of only one kind of atom, e.g. oxygen (O2)
• A molecule is a group of atoms bound together to form a larger chemical unit, e.g. H2O
• A compound refers to substances whose molecules have more than one kind of element, e.g. CO2, NaCl

Important Elements in the Human Body

• Living organisms require about 20 elements
• Oxygen, carbon, hydrogen, and nitrogen are the most abundant, comprising 96%

Chemical Bonding

• Chemical bonds form to make atoms more stable
• An atom with a full outer shell is a chemically stable atom and unlikely to form a bond with another atom
• 'Stability’occurs through sharing, donating, or borrowing electrons
• Chemical 'bonds' can be ionic or covalent

Ionic Bonds

• Form between an atom that only has 1 or 2 electrons in its outermost energy level, which normally holds 8
• Also forms between an atom that only needs 1 or 2 electrons to fill its outermost energy level
• An atom with 1 or 2 electrons donates them to the other

Definition: Ion

• Ion is an atom or group of atoms with an electrical charge (+ or -)
• Ions form when an atom gains or loses electrons in its outer energy level to become stable
  • Positive ion has lost electrons, indicated by a superscript positive sign(s), as in Na+ or Ca+
  • Negative ion has gained electrons, indicated by a superscript negative sign(s), as in Cl-

Ionic Bonds

• Ionic bonds form when positive and negative ions attract each other because of electrical attraction

Electrolytes

• Ionic molecules usually dissolve in water and dissociate to form free ions (electrically charged)
• Electrolyte is a molecule that dissociates, or breaks apart, in water to form individual ions, e.g. Na+, Cl-

Covalent Bonds

• Form when atoms fill their energy levels by sharing electrons to become stable
• For atoms to share, they must stay close to each other, therefore, bonds do not easily break/dissociate in water

Hydrogen Bond

• Provides subtle forces that help to keep larger molecules in a certain configuration (e.g., H20)

Organic vs Inorganic Compounds

• Organic compounds contain carbon–carbon covalent bonds and/or carbon–hydrogen covalent bonds
• Inorganic compounds do not
  • Examples: water, some acids, bases, and salts

Water (H2O)

• Is a solvent, a liquid into which solutes are dissolved, that forms aqueous solutions in the body
• Involved in chemical reactions
  • Dehydration synthesis: water is removed from small molecules so they can be strung together to form a larger molecule
  • Hydrolysis: water is added to the subunits of a large molecule to break it apart into smaller molecules

Chemical Reactions

• Always involve energy transfers
• Some of the energy is stored in bonds and released when bonds are broken (e.g. ATP)
• Chemical equations are often used to illustrate reacants, products and direction of reaction, e.g., K+ + Cl- ⇾ KCl

Acids, Bases and Salts

• Water molecules dissociate to form equal amounts of H+ (hydrogen ion) and OH– (hydroxide ion)
  • In pure water, H+/OH– balance is equal
  • This is not the case with acids and bases
• Acid refers to a substance that shifts the H+/OH– balance in favor of H+ and is the opposite of base
• Base refers to a substance that shifts the H+/OH– balance against H+ and is also known as an alkaline and is the opposite of acid

pH (Potential of Hydrogen)

• pH is a mathematical expression/unit of measurement used to express the H+ concentration of a solution
  • A pH of 7 is neutral, neither acidic nor basic
  • Anything above 7 is basic
  • Anything below 7 is acidic